The present invention relates to transmission schemes for wireless digital communication systems, and more particularly to high order modulation based on improved signal constellation and bit labeling designs for enhanced performance, including decreased power consumption.
In wireless communication systems, higher order modulation enables transmission of more than two bits in a symbol with more signal power, reducing the transmission bandwidth required. Modern communications systems typically use phase shifted keying (PSK)-based modulation and coherent demodulation to reduce transmit power. Higher order modulation generally employs more than 4 possible phases and more than one signal amplitude to send more than 2 bits in a phase/amplitude symbol. A signal constellation diagram is a representation of a signal modulated by a digital modulation scheme, such as quadrature amplitude modulation or phase-shift keying. The signal constellation depicts the signal as a two-dimensional scatter diagram, in the complex plane, at symbol sampling instants. In other words, the signal constellation represents the possible symbols that may be selected by a given modulation scheme as points in the complex plane. Accordingly, a modulated waveform, from a set of data symbols, leads to the concept of a signal constellation. In addition to optimizing modulation, it is well-known that significant power reduction can be achieved by applying forward error correction (FEC) coding to the information.
Well-known classical examples of higher order modulation signals include 8-PSK, 16-QAM, 32-QAM and 64-QAM, which are capable of sending 3, 4, 5 and 6 bits, respectively, per symbol. For satellite transmission, because power is at its premium, the 16-QAM, 32-QAM and 64-QAM signals are often modified by organizing them to several rings of different amplitudes. The Digital Video Broadcast via Satellites standard (DVB-S2) employs 16-APSK and 32-APSK modulation signals, where the 16-APSK employs a signal constellation of two rings, with 4 and 12 possible phase positions, respectively, and the 32-APSK employs a signal constellation of three rings, with 4, 12 and 16 possible phase positions, respectively. As such, they are also called 4+12-APSK and 4+12+16-APSK, respectively.
While current signal constellations, including the signal constellations of the DVB-S2 standard, perform to a reasonably acceptable level, however, improved signal constellations with appropriate bit labeling are possible, resulting in improved performance characteristics, including reduced power consumption.
It is, therefore, desirable to have high order modulation based on improved signal constellation and bit labeling designs for enhanced performance characteristics, including decreased power consumption.